Surface watercraft

ABSTRACT

A general wing form to be used as a stabilizer for watercraft or as a double hulled craft in itself. It is comprised of two buoyant foil or hull elements and a connecting beam, and characterized by its integral structure, its anhedral configuration and its particular use of static and dynamic left forces for stability.

D United States Patent 1191 1111 3,742,887

Russell July 3, 1973 SURFACE WATERCRAFT 2,745,370 5/1956 Manis 114/61 x [76] Inventor: Diana Russell, 167 E. 99 St., Apt.

A4, New York, 10029 Primary Exammer-M1lton Buchler Assistant Examiner-Stuart M. Goldstein Flledi 1 Attorney-David Brinkman [21] Appl. No.: 99,016

[57] ABSTRACT 521 US. Cl. 1 14/61 A general wing form to be used as a liz r for water- [51] Int. Cl. B6311 1/00 craft or as a double hulled Craft n lf. It is comprised [58] Field 61 Search 114/61, 123 of two buoyant foil or hull elements and a Connecting beam, and characterized by its integral structure, its [56] References Ci d anhedral configuration and its particular use of static and dynamic left forces for stability.

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sum 3 or 3 7 ATTORNEY SURFACE WATERCRAFT BACKGROUND OF THE INVENTION This invention relates generally to the design and construction of curved foils as hulls or stabilizers for surface craft.

The point of maximum stability of a conventional catamaran occurs at a small angle of heel. As the heel angle increases beyond this point, the buoyant righting moment of the craft decreases. The connecting beams between the two hulls contribute very little buoyancy. The points at which they are joined to the hulls, however, are subject to extra structural stresses.

Similarly, with a pontoon stabilizer system on a trimaran, the connecting beams contribute negligible righting force in themselves. Beyond a certain heel angle, the stability decreases continuously.

Most conventional applications of hydrofoils either as stabilizers or as bearing surfaces for watercraft (either power or sailing) entail complex structural configurations. They are designed for maximum efficiency of the individual articulated foil elements. The systems generally include struts which are structurally but not hydrodynamically functional. They generally provide self-correcting mechanisms to compensate for pitch and roll of the craft. These systems are particularly subject to extra stresses at those points where the elements are connected.

In general, some of the benefits of the above forms are partially offset by inherent disadvantages of discontinuity in the structure and displacement of the forms.

The present inventor is aware of the following United States Patents relating to surface craft foils, hulls and stabilizers:

2,745,370 Manis, Stable Water Jet Hull 3,112,725 Malrose, Triscaph 3,223,066 Irving, Boat Structure 3,274,966 Rethorst, Water Surfing Craft 3,295,487 Smith, I-Iydrofoil Sailboat 3,455,264 Castellani, Wing Bearing Craft 3,459,149 Prior, I-Iydrofoil Watercraft De. 214,766 Alter, Sailing Catamaran.

SUMMARY OF THE INVENTION This wing form, in its simplest and most direct embodiment, includes a single span (two sided surface) curved so the tips of the span pierce the surface of the water and the middle part of the span remains clear of the water. The tips of the span are buoyant foils, the bearing surfaces of the structure, canted anhedrally, while the middle is the connecting beam and load bearing platform of the structure. The span may be used as a stabilizer affixed to a single hulled craft, or it maybe used as a double hulled craft in itself. The particular use determines the specific span to chord or beam to length ratio of the form and also the camber or symmetry of the foil section or hull waterline. It also determines any possible structural modifications of the form that do not interfere with the essential elements: the two curved anhedral foils and the connecting beam.

The two bearing surfaces develop dynamic lift or act as displacement forms according to the foil proportions and the velocity of the craft. As the lift due to dynamic effects increases, the depth of immersion of the foils decreases.

There is provided in accordance with the principles of the invention a form which incorporates features of either a displacement craft or a foil stabilizer in a structurally integral system of continuous surfaces.

When the curved foil form (of the invention) is used as a stabilizer for a sailing craft, it permits a higher speed potential than is possible for a conventional pontoon stabilized trimaran. Substituting the curved foil for a displacement type outrigger pontoon can reduce the total wetted surface area of the moving craft when it is subject to heeling forces. The wing can be completely clear of the waters surface when the craft is not heeling or rolling.

The invention provides a stabilizer that derives its righting moment from dynamic forces so that its effectiveness at any speed is not diminished by the shortening of the buoyant righting arm at greater angles of heel.

Also, when the foil is used as a stabilizer for a sailing craft, it is less subject to flipping (due to sudden gusts of wind) characteristic especially of catamarans. The initial stability of a craft with a wing form stabilizer is lower than that of a conventional multihull craft. The dynamic righting forces will not respond instantaneously to gusts of wing as the craft cannot accelerate instantaneously. However, the static buoyant force (displacement volume) of the wing increases inboard as its moment arm decreases. This produces a sailing craft that is less stiff" than a conventional catamaran or trimaran whose maximum stability is in a position more nearly upright. Thus the wing stabilized craft will be able to heel more initially in response to a sudden gust and dump" some of the wind from its sails without exceeding its position of maximum stability.

When the wing form is used as a double hulled craft in itself, it can have the structural simplicity of a scow with almost the stability of a catamaran. The disadvantage of slightly lower initial stability is offset by the increase in buoyant righting force with angle of heel and decrease in righting arm.

When the catamaran version of the wing form is supplemented with high lift hydrofoils between the keels of the two hulls, it can have the virtues of an integral hull structure in addition to certain of the advantages of a hydrofoil catamaran over a monohull hydrofoil craft. The reserve buoyancy in the bulls damps the vertical accelerations due to variations in effective trim angle with respect to wave phase, thus reducing the need for a complicated control system to regulate the trim angle. Because the bulls partially shield the foils, the craft is less subject to damage or interference from floating or submerged objects than a conventional hydrofoil craft.

Generally, whether the wing form is used as either a stabilizer or as a double hulled craft, it provides structural strength and freedom from a multitude of specific local stress areas. The The continuous curve of the wing particularly lends itself to construction in fiberglas-reinforced plastics, a form simply comprising two molded skins joined together at their coincident edges. The only point of localized stress will occur at this edge of the complete form. Furthermore, its design is such that the maximum section thickness occurs at the middle of the span, the area of maximum stress due to bending moments developed by the payload and the two bearing surfaces. This represents some improvement over conventional catamaran construction and hydrofoil stabilizer configurations.

The accompanying drawings illustrate several presently preferred embodiments of the invention and illustrate its principles.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view of the wing form with a forward quarter broken away and sectioned to expose exempliary interior details. FIG. 1 is drawn to a larger scale than FIGS. 2 4.

FIG. 2 is a side elevational view of the wing form.

FIG. 3 is a sectional view of the wing form along the line 3-3 in FIG. 2.

FIG. 4 is a plan view of the wing form used as a double hulled craft in itself.

FIG. 5 is a plan view of the wing form used as a stabilizer for a sailing craft.

FIG. 6 is a sectional view of the stabilizer wing form along the line 6-6 in FIG. 7.

FIG. 7 is a lateral cross-section of the wing form as a stabilizer on the sailing craft of FIG. 5 drawn to a smaller scale.

FIG. 8 is a front elevation of the catamaran wing form with hydrofoils between the two keels.

FIG. 9 is a side elevation of the hydrofoil catamaran.

FIG. 10 is a schematic lateral cross-section of an upright vee hull.

' FIG. 11 is a schematic lateral cross-section of a vee hull heeled at an angle of B B with respect to vertical.

FIG. 12 is a schematic lateral cross-section of a foil with its span-chord plane oriented vertically.

FIG. 13 is a schematic lateral cross-section of a foil with its span-chord plane canted at an angle of )3 B from vertical.

NOTATION In the drawings, description and claims, the symbols used are defined as follows:

A Aspect ratio, X/Y or XIS X Beam of hydrofoil or planing surface, span of hydrofoil CL Coefficient of hydrofoil lift, L l rpS V O Coefficient of planing lift, L,,/%pS,,V

Z Depth of foil or hull immersion below water line L, Lift developed by hydrofoil portion of surface 1b.

L, Lift developed by planing portion of surface, 1b.

Y Means wetted length of foil or planing surface,

chord of hydrofoil S Horizontally projected (lifting) surface of hydrofoil S, Horizontally projected (lifting) surface area of planing portion of surface ST Total wetted surface of hydrofoil, S, sec B S sec or S Total wetted area of planing surface, S, sec B S,- Total wetted surface of foil, S -S V Horizontal velocity of craft WL, Water line at velocity V a Angle (acute) between water line and tangent to upper surface of foil B Angle of deadrise, degrees, between water line and tangent to lower surface of foil p Mass density of water, 1.98 slugs/cubic foot 1 Trim angle, degrees, measured longitudinally between bottom surface and horizontal A Weight displacement of foil or hull, one-half wing form, lb.

VVolume displacement, cu. ft., of foil or hull at rest Volume displacement, cubic feet, of foil or hull at velocity V.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Referring to the drawings, it will be seen that the stabilizer variation and the double hulled craft variation of the general wing form have in plan view (FIG. 4. and FIG. 5.) substantially different proportions of lateral cross section to longitudinal section dimensions. However, the principle of the form is adequately shown in FIGS. 1., 2., and 3. without regard to those specific proportions.

FIG. 1. shows a lateral cross section of the general form. WL, denotes the water line at any velocity V and at any angle of heel. The buoyant foil or hull elements of the form are defined as the portion(s) below the water line WL, or submerged at any given time. The connecting beam is defined as the connecting portion between the two foils or hulls and above the water line WL,,. Its outer surfaces or skins are continuous and smoothly merging with those of the foils or hulls.

FIG. 2. shows the form in longitudinal profile. The view shows the form without an additional hull centrally disposed between the two foils. Thus it illustrates in profile the general form by itself or used as a double hulled craft. FIG. 3. shows a generalized longitudinal section of the form. FIG. 4. shows a plan view of a wing form specifically designed to be used as a double hulled craft in itself.

FIGS. 5., 6. and 7. illustrate the use of the wing form 10 specifically as a stabilizer attached to a water craft 30. In the case that the foil part of the stabilizer is designed to develop dynamic lift, the wetted area of the submerged foil, section DAC in FIG. 1. extended longitudinally, will depend on the depth of immersion i of the foil, which in turn will depend on the total (buoyant and dynamic) lift force on the foil. Thus as the craft accelerates, subject to a constant wind force on the sail 32, and the dynamic lift force increases, the depth of immersion and the wetted area of the foil decrease. A conventional centerboard 34 and rudder 36 are shown provided on the water craft 30.

The section shown in FIG. 1. represents the structural design most particularly appropriate to the form 10 in general. The anhedral disposition of the foils 12, 14 permits the use of an integral connecting beam 16 consisting of two curved, molded skins 18, 20 continuous with the surfaces of the two foils or hulls, thus minimizing the number of points of discontinuously large stress in the structure. Removable longitudinal sections 22, 24 and crosswise through bolts 26 permit adjustment of the cant of the foils and the span of the form. This form satisfies the requirements for fiberglass reinforced plastic construction mentioned earlier. The fiberglass skin can be stiffened with either foam structural members or a solid foam core 28. Furthermore, its streamline shape also minimizes incidental form drag in conditions of extra load or heeling. Particular applications and hydrodynamic design considerations will determine proportions and precise curvature of the form as well as size, shape and details of the removable sections in any specific design.

FIGS. 8. and 9. show an example of a specialized application, a catamaran version of the wing form with high lift hydrofoils 40 between the two hulls of the craft.

The following discussion is offered as a theoretical explanation of certain principles of the invention. The definitions used are ad hoc and informal, not necessarily in accordance with the strict principles of hydrodynamics, but sufficiently explained in the text. Although portions of the theory may eventually prove to be in er-' ror, the discussion should be of assistance to those skilled in the art in developing a full understanding of the invention.

DYNAMIC LIFT As the form is symmetric about the centerlineQ .consideration of static and dynamic lift forces on one of the two foils will be sufficient for an analytical discussion.

The static buoyant lift A of one foil at a constant velocity V is equal to the displacement volume Yiof the foil (cubic feet) times the weight of one cubic foot of water B (62.4 pounds), or, more concisely, A =7 where A one-half the total weight of the form.

The total dynamic lift developed by the foil (DAC section) is equal to the sum of the planing lift and the hydrofoil lift or:

The sum of dynamic lift L and buoyant lift A of the foil section DAC at a constant velocity V is equal to onehalf the total displacement weight -2 A of the form:

The planing lift forces developed by the foil depend on the length, beam, deadrise angle and trim angle of the planing surface. The beam of the planing surface is defined as the horizontal distance X, in FIG. 1. between points B and C, where a portion of the lower surface of the foil at the specific section is below the water line WL, and the vertically projected portion of the upper surface of the foil, between points D and E, is above the water line WL,,. The deadrise angle B, at a velocity V, is defined as the angle between the water line WL, and the line tangent to the lower surface of the foil at the water line (point C). l, in FIG. 2. represents the mean wetted length of the foil. r in FIG. 2. represents the trim angle of the form and of the foil.

The planing lift force L, (in FIG. 1.) on the foil can be determined using the above definition of the planing portion of the surface (section DBCE) and the formula for planing liftz L, C kpS V where p is mass density of water, slugs/cu.ft. V is velocity S, is horizontal surface area (subject to planing lift),

X, L, C is the coefficient of planing lift based on 1, B and aspect ratio A. The notion of planing lift on a foil surface is more clearly shown with reference to the schematic drawings of hull and foil sections, FIGS. 10., 11., 12., and 13. The vee-hull and foil section can be compared as follows; the foil section can be considered as deeper, narrower version of the vee-hull, heeled to one side. This reduces'B on the right hand side of the section view, so that B becomes B, and increases one-half of the planing beam so that X becomes X thus increasing the lift force on that side. For a conventional hull, that part of the surface whose upper portion is below the water line and has angle of deadrise greater than 90 would be considered to have negative lift contributing to an unstable situation. Only section X could bg considered to be giving a positive lift contribution Li; and that lift would be reduced by some amount VLLQC'IEOT)" 24,. However, for a foil section, the beam segment b 09 would develop positive lift which would be increased by a positive lift contribution from the segment X X, because of the longitudinal trim and camber of the foil.

The semi-planing foil section has two limiting cases: one, a fat foil section with the outside surface vertical a such that the hydrofoil lift component is equal to 0; two, a skinny foil section canted at a high deadrise angle B such that the planing lift force component is negligible.

The hydrofoil lift forces developed by the submerged portion of the foil depend on the beam, length, deadrise angle and trim angle of the foil surface. The beam of the hydrofoil surface is defined as the horizontal distance in FIG. 1., between points A and B, where a portion of the lower surface of the foil at the specific section is below the water line WL,,, and the vertically projected portion of the upper surface of the foil, between points A and D, is also below the water line WL,,. The deadrise angle B is, for purposes of simplified calculation, adequately defined as the same B as for the planing portion of the foil surface, the angle between the water line WL,,, and the line tangent to the lower surface of the foil at the water line (point C).l,, in FIG. 2. represents the mean wetted length of the foil. 1' in FIG. 2. represents the trim angle of the foil.

The hydrofoil lift force L (FIG. I.) can be determined using the above definition of the hydrofoil portion of the foil surface (section DAB) and the formula for hydrofoil lift:

p is mass density of water, slugs/cu.ft. V is velocity, 8,, is horizontal surface area subject to hydrofoil lift (S X, I and I C is the coefficient of hydrofoil lift based on foil aspect ratio and chamber. The total wetted area S of the foil is equal to the sum of the total area S sec B of the planing portion of the foil surface plus the total area S,, (sec B sec or of the hydrofoil portion of the foil surface.

S S sec B S,, sec B S,, see a It can be seen from FIGS. 1. and 2. that total wetted area S, is a function of the depth of immersion Z of the foil, as is also the submerged volume V,,, and that Z, in turn, is a function of the velocity V. Thus the wetted area of the foil is reduced as the craft accelerates.

Hydrodynamic design considerations in determining the precise curvature of the form include a reduction in the deadrise angle B at the upper part of the section where planing force is contributing to vertical lift. A reduced B will increase the dynamic lift force and also add to the reserve buoyancy and initial displacement volume. The tips of the foils could be somewhat flared to increase the lifting area under small displacement volume conditions.

What is claimed is:

1. A wing form comprising two water-buoyant, air/- water interfacial surface-piercing foils, each having means defining an inside and an outside opposing,

bearing surfaces, said foils being canted downwardly dihedrally;

and at least one connecting beam extending clear of the air/water interfacial surface between the two foils, said connecting beam having means defining an inside, generally horizontal lower surface and an outside, upper surface; the outside surface of said connecting beam being continuous with and smoothly merging with the corresponding outside surfaces of the two foils; the inside surface of said connecting beam being continuous with and smoothly merging with the corresponding inside surface of the two foils, there being thereby provided a wing form which is downwardly concave along both the outside, upper surface thereof and the inside, lower surface thereof.

2. The form of claim 1. further including a watercraft disposed centrally between the two foils; said watercraft being secured to said connecting beam; said foils being so positioned relative to said watercraft that said foils pierce the air/water interfacial surface only when the watercraft rolls or heels.

3. The form of claim 1. wherein said two foils constitute hulls; the form further comprising means for steering said hulls and means for propelling said form.

4. The form of claim 1. further including means for adjusting the cant of said foils.

5. The form of claim 1. further including means for adjusting the span of said of said form.

UNITED STATES PATENT oEETc CERTlFlCATE 01F CORRECTION E Patent No. 3,7" 7 Dated July 3, 973

Inventor s DIANA RUSSELL It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

ABSTRACT Line 6, "dynamic left forces" should be changed to --dynamic lift f0Ices--;

Column 2 line 23, change gusts of wing" to --gusts of wind";

Column 3, line L 4, change "lb to ---lbs .---5

line #5, change "1b" to --1.bs line 46, change "Y" to -l --3 change "Means" to ---Mean---;

Column l, line 36, change "immersion i" to "immersion Z-;

11 H Column 6, line 4, ,hange L( r r) to L 1 line 5, change "b to X delete "2 T";

P line 6, delete "09''; line 20, change to -X -5 Column 8, line l l, after "span oi sea id dele te second "of said".

Signed and sealed this 27th. day of November 1973'.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents 

1. A wing form comprising two water-buoyant, air/water interfacial surface-piercing foils, each having means defining an inside and an outside opposing, bearing surfaces, said foils being canted downwardly dihedrally; and at least one connecting beam extending clear of the air/water interfacial surface between the two foils, said connecting beam having means defining an inside, generally horizontal lower surface and an outside, upper surface; the outside surface of said connecting beam being continuous with and smoothly merging with the corresponding outside surfaces of the two foils; the inside surface of said connecting beam being continuous with and smoothly merging with the corresponding inside surface of the two foils, there being thereby provided a wing form which is downwardly concave along both the outside, upper surface thereof and the inside, lower surface thereof.
 2. The form of claim
 1. further including a watercraft disposed centrally between the two foils; said watercraft being secured to said connecting beam; said foils being so positioned relative to said watercraft that said foils pierce the air/water interfacial surface only when the watercraft rolls or heels.
 3. The form of claim
 1. wherein said two foils constitute hulls; the form further comprising means for steering said hulls and means for propelling said form.
 4. The form of claim
 1. further including means for adjusting the cant of said foils.
 5. The form of claim
 1. further including means for adjusting the span of said of said form. 